ES2751276T3 - Process to produce acetic acid - Google Patents

Abstract

A process for producing acetic acid comprising: carbonylating at least one reagent selected from the group consisting of methanol, dimethyl ether, methyl acetate and mixtures thereof, in the presence of 0.1 to 14 wt% water, a metal catalyst, methyl iodide and iodide salt to form a reaction medium in a reactor; separating the reaction medium into a recycled liquid and a vapor product stream including acetic acid, methyl iodide, methyl acetate and water; condensing a first portion of the steam product stream to form a liquid stream; feeding a second portion of the steam product stream to a first column; feeding at least a portion of the liquid stream to the first column; and extracting a side stream from the first column comprising an acetic acid product; wherein the liquid stream is fed to the first column above the supply of the second portion of the steam product stream and wherein the liquid stream is fed to the first column below the point where the side stream comprising the acetic acid product is drawn from the first column.

Description

DESCRIPTION

Process to produce acetic acid

Related request

The present application claims priority over the US Provisional Application. Serial No. 62 / 058.936 filed on October 2, 2014.

Background

Among the processes currently used to synthesize acetic acid, one of the most commercially useful is carbon monoxide catalyzed carbonylation of methanol as taught in US Pat. No. 3,769,329. The carbonylation catalyst contains a metal catalyst, such as rhodium, that is dissolved or otherwise dispersed in a liquid reaction medium or supported on an inert solid, together with a halogen-containing catalyst promoter, as exemplified by means of methyl iodide. More normally and usefully, the reaction is carried out by continuously bubbling carbon monoxide gas through a liquid reaction medium in which the catalyst is dissolved.

Methanol and carbon monoxide are fed into a reactor as raw material. A portion of the reaction medium is continuously withdrawn and provided to an instant vaporizer where the product is instantly vaporized and sent as a vapor to a purification train. The purification train includes a column of light end products that removes the "light" or low boiling components as a head product and provides a side stream for further purification. The purification train may additionally include columns to dehydrate the side stream or to remove "heavy" or high boiling point components, such as propionic acid, from the side stream. It is desirable in a carbonylation process to make acetic acid to minimize the number of distillation operations to minimize the use of energy in the process, US Pat. No. 5,416,237 discloses a process for the production of acetic acid by carbonylation of methanol in the presence of a rhodium catalyst, methyl iodide and an iodide salt stabilizer. The improvement according to the '237 patent resides in maintaining a finite concentration of water of up to about 10% by weight and a concentration of methyl acetate of at least 2% by weight in the liquid reaction composition and recovering the product of acetic acid by passing the liquid reaction composition through an instantaneous vaporization zone to produce a vapor fraction that is passed to a single distillation column from which the acetic acid product is removed. The drawback of eliminating the distillation steps is that the purity level of the product suffers. In particular, distillation columns tend to remove high boiling iodides as well as aldehyde contamination products. Both impurities affect the commercial suitability of the final product.

US Patent No. 6,657,078 discloses a low energy process for producing acetic acid by carbonylation of methanol. The process involves a rhodium catalyzed system that works with less than about 14% by weight of water using up to 2 distillation columns.

The US publication No. 2013/0116470 discloses an acetic acid production process comprising a reaction step to continuously allow at least one member selected from the group consisting of methanol, dimethyl ether and methyl acetate to react with carbon monoxide in a catalyst system comprising a rhodium catalyst, a salt of iodide and methyl iodide in the presence of acetic acid and water in a plant involving a reactor, an instant vaporizer and a distillation column, and in which part of the vaporized stream is introduced into a heat exchanger. The liquid portion that condenses from the vaporized stream is returned to the reactor for cooling purposes. As a result of the need to cool the reactor, the process disclosed in the US Pub. No. 2013/0116470 increases the recycling of acetic acid, reducing the efficiency of carbon monoxide.

A frequent production limitation in the purification section of an acetic acid unit is the light end product column. In a typical carbonylation process of methanol and acetic acid, the high pressure hot liquid from the reactor is reduced in pressure through a valve and subjected to instantaneous vaporization in a lower pressure instantaneous vaporization vessel. The vapors released at this stage are fed near the bottom of a column of light end products. Condensed liquids rich in acetic acid are removed from a liquid side extraction above the feed and fed forward for further purification, while the vapors leaving the tower head product are condensed and fed to a decanter liquid-liquid. The light phase from the decanter flows back to the tower and the heavy phase is recycled to the reactor feed. Thus, the light end product column receives a stream of hot vapor product from the flash vapor and operates by removing most of the methyl acetate and methyl iodide from the stream before the product stream is fed forward for the withdrawal of water. US Patent No. 8,173,076 describes an improved apparatus and method for producing acetic acid that includes condensing overhead product vapor to provide reflux to the column of light end products, as well as condensing vapor from a central portion of the end product column. light to increase the capacity. WO 2013/137236 A1 discloses a method of producing acetic acid.

Therefore, what is needed is an improvement in an acetic acid production process that does not result in increased recycling of acetic acid and improves the performance of the light end product column.

Summary

The present invention relates to a process for producing acetic acid comprising:

carbonylate at least one reagent selected from the group consisting of methanol, dimethyl ether, methyl acetate and mixtures thereof, in the presence of 0.1 to 14 wt% water, a metal catalyst, methyl iodide and salt iodide to form a reaction medium in a reactor;

separating the reaction medium into a recycled liquid and a vapor product stream including acetic acid, methyl iodide, methyl acetate and water;

condensing a first portion of the steam product stream to form a liquid stream; feeding a second portion of the steam product stream to a first column;

feeding at least a portion of the liquid stream to the first column; Y

extracting a side stream from the first column comprising an acetic acid product; wherein the liquid stream is fed to the first column above the feed of the second portion of the steam product stream and wherein the liquid stream is fed to the first column below the point where the side stream comprising the acetic acid product is drawn from the first column.

In a first embodiment, the present invention relates to a process for the production of acetic acid comprising carbonylating at least one reagent selected from the group consisting of methanol, dimethyl ether, methyl acetate and mixtures thereof, in the presence of 0.1 to 14 wt% water, a metal catalyst, methyl iodide, and iodide salt to form a reaction medium in a reactor and separate the reaction medium into a recycled liquid and a vapor product stream that includes acetic acid, methyl iodide, methyl acetate, and water. The process further comprises condensing a first portion of the steam product stream, ie, 1 to 50%, to form a liquid stream and a steam stream; feeding a second portion of the steam product stream, i.e. 50 to 99%, to a first column, feeding part or all of the liquid stream, preferably at least 10%, to the first column and extracting a side stream comprising an acetic acid product from the first column, in which the liquid stream is fed to the first column above the feed of the second portion of the steam product stream and in which the stream Liquid is fed to the first column below the point where the side stream comprising the acetic acid product is withdrawn from the first column. In one embodiment, the process comprises feeding the side stream to a second column to obtain a purified acetic acid product. Part of the liquid stream can be introduced into the second column. The liquid stream can be enriched in acetic acid compared to the second portion of the steam stream and comprises acetic acid from 65 to 95% by weight. In one embodiment, the liquid stream is not returned to the reactor and the reactor has a cooling unit, such as a pump circuit. The process of the present invention advantageously maintains the efficiency of carbon monoxide in the reactor above 90%.

Also described is a process for the production of acetic acid comprising carbonylating at least one reagent selected from the group consisting of methanol, dimethyl ether, methyl acetate and mixtures thereof in the presence of 0.1 to 14% water in weight, a metal catalyst, methyl iodide, and iodide salt to form a reaction medium in a reactor and separate the reaction medium into a recycled liquid and a vapor product stream including acetic acid, methyl iodide, acetate of methyl and water in a flash tank that has an optional top wash section. The process further comprises condensing a first portion of the steam product stream, for example 1 to 50%, to form a liquid product stream and a steam stream, feeding a second portion of the steam product stream, for example, from 50 to 99%, to a first column, withdraw a side stream comprising an acetic acid product from the first column to a second column, feed part or all of the liquid product stream, preferably at least 10% to the second column and obtain a purified acetic acid product from the second column. In one embodiment, part of the liquid stream can be introduced into the first column. The liquid stream can be enriched in acetic acid and comprise acetic acid from 65 to 95% by weight. In one embodiment, the liquid stream comprises an amount equal to or greater than that of acetic acid in the side stream, for example, greater than 90%. In one embodiment, the liquid stream is not returned to the reactor and the reactor has a cooling unit, such as a pump circuit. The process of the present invention advantageously maintains the efficiency of carbon monoxide in the reactor above 90%.

Brief description of the drawings

The present invention will be better understood in view of the attached non-limiting figures, in which:

FIG. 1 is a schematic drawing of the condensation vapor product stream to produce a liquid stream that is introduced into a first column according to embodiments of the process disclosed herein; Y

FIG. 2 is a schematic drawing of steam product stream condensation to produce a liquid stream which is introduced into a second column in accordance with alternative embodiments disclosed herein.

Detailed description

Introduction

In the summary and in the present detailed description, each numerical value must be read once as modified by the term "approximately" (unless it has already been expressly modified in this way) and then read again as not modified in this way at Unless otherwise stated in context. Furthermore, in the summary and in the present detailed description, it should be understood that in a concentration range listed or described as useful or adequate, it is to be considered that each and every concentration within the range has been indicated, including the points endings. For example, an interval "from 1 to 10" should be read as indicating each and every possible number along the continuum between approximately 1 and approximately 10. Therefore, even if specific data points are explicitly identified within of the range, or even if no data point is explicitly identified within the range, or if only a few specific data points are referenced, it is to be understood that the inventors appreciate and understand that each and every point of Data within the range are to be considered specified and that the inventors were aware of the full range and all points within the range.

Throughout the entire specification, including the claims, the following terms have the meanings indicated unless otherwise specified.

As used in the specification and claims, "near" includes "in". The term "and / or" refers to both the inclusive case "and" and the exclusive case "or", and is used herein for brevity. For example, a mixture comprising acetic acid and / or methyl acetate can comprise acetic acid alone, methyl acetate alone, or both acetic acid and methyl acetate.

All percentages are expressed as a percentage by weight (% by weight), based on the total weight of the present stream or particular composition, unless otherwise indicated. The ambient temperature is 25 ° C and the atmospheric pressure is 101,325 kPa unless otherwise indicated.

For the purposes of this document:

Acetic acid can be abbreviated as "AcOH";

acetaldehyde can be abbreviated as "AcH";

methyl acetate can be abbreviated "MeAc";

methanol can be abbreviated "MeOH";

methyl iodide can be abbreviated as "Mel";

hydrogen iodide can be abbreviated as "HI";

carbon monoxide can be abbreviated "CO"; Y

HI refers to molecular hydrogen iodide or dissociated hydroiodic acid when it is at least partially ionized in a polar medium, usually a medium comprising at least part of water. Unless otherwise specified, the two are referenced interchangeably. Unless otherwise specified, the HI concentration is determined through acid-base titration using a potentiometric endpoint. In particular, the HI concentration is determined by titration with a standard solution of lithium acetate to a potentiometric end point. It is to be understood that for the purposes of this document, the HI concentration is not determined by subtracting a concentration of iodide that is assumed to be associated with a measurement of corrosion metals or other non-H + cations of the total ionic iodide present in a sample.

It is to be understood that the HI concentration does not refer to the iodide ion concentration. HI concentration refers specifically to the HI concentration determined through potentiometric titration.

This subtraction method is an unreliable and imprecise method of determining relatively lower HI concentrations (i.e. less than about 5 weight percent) due to the fact that all non-H + cations (such as Fe, Ni, Cr, Mo cations) are associated with the iodide anion exclusively. In reality, a significant portion of the metal cations in this process may be associated with the acetate anion. Additionally, many of these metal cations have multiple valence states, adding even more unreliability to the assumption about the amount of iodide anion that might be associated with these metals. Ultimately, this method results in an unreliable determination of the actual HI concentration, especially in view of the ability to perform a simple test that is directly representative of the HI concentration.

For the purposes of this document, a "head product" or "distillate" from a distillation column refers to at least one of the lower boiling condensable fractions that exits at or near the top (eg, near the top) of the distillation column, and / or the condensed form of that stream or composition. Obviously, all fractions are ultimately condensable, however, for the purposes of this document, a condensable fraction is condensable under the conditions present in the process, as one skilled in the art readily understands. Examples of non-condensable fractions can include nitrogen, hydrogen, and the like. Similarly, a head product stream may be taken just below the highest outlet of a distillation column, for example, where the lowest boiling fraction is a non-condensable stream or represents a de minimis stream, as you would easily understand a person of reasonable skill in the matter.

The "bottoms" or "residues" of a distillation column refer to one or more of the highest boiling fractions leaving at or near the bottom of the distillation column, also referred to herein as " they flow from the sump at the bottom of the column. It is to be understood that a residue may be taken just above the outlet of the lower part of a distillation column, for example, in which the fraction of the lower part produced by the column is a salt, an unusable tar, a solid waste product or a de minimis stream as a person of reasonable skill would readily understand.

For the purposes of this document, the distillation columns comprise a distillation zone and a bottom sump zone. The distillation zone includes everything above the bottom sump area, that is, between the bottom sump area and the top of the column. For the purposes of this document, the bottom sump area refers to the bottom portion of the distillation column where a liquid reservoir of the highest boiling point components is present (for example, the bottom from a distillation column) from which the bottom or residual stream flows after leaving the column. The bottom sump area may include evaporators, control equipment, and the like.

It is to be understood that the terms "passages", "flow paths", "flow conduits", in relation to the internal components of a distillation column, are used interchangeably to refer to orifices, tubes, channels, slits, drains, that are arranged through and / or that provide a path for liquid and / or vapor to move from one side of the internal component to the other side of the internal component. Examples of passages arranged through a structure such as a liquid distributor in a distillation column include drain holes, drain tubes, drain slits, and the like, which allow a liquid to flow through the structure on one side. to another.

The average residence time is defined as the sum total of the entire volume of liquid retained for a given phase within a distillation zone divided by the average flow rate of that phase through the distillation zone. The retention volume for a given phase can include the volume of liquid contained in the various internal components of the column, including the collectors, distributors, as well as the liquid contained in trays, inside downspouts and / or within compacted bed sections structured or random.

The present disclosure relates to processes for producing acetic acid and reducing recycling of acetic acid to the reactor. The process provides a method of removing acetic acid from a condensed, i.e., liquid stream, of a vapor product stream before it is returned to the reactor. The liquid stream is enriched in acetic acid compared to the vapor product stream and therefore it is more advantageous to recover acetic acid by feeding part or all of the liquid stream to a first and / or second column column. In some embodiments, part of the liquid stream can be returned to the reactor. Advantageously, by introducing an enriched acetic acid liquid stream into the first column and / or the second column, the operation of those columns can be improved. In particular, the first column may not have a bottleneck without significantly changing the composition of the side stream.

In embodiments, the liquid stream from the condensed steam product stream is fed to a first column. The process for producing acetic acid according to a first embodiment of the present invention comprises carbonylating at least one reagent selected from the group consisting of methanol, dimethyl ether, methyl acetate and mixtures thereof, in the presence of 0 water, 1-14% by weight, a metal catalyst, methyl iodide and iodide salt to form a reaction medium in a reactor; separating the reaction medium into a recycled liquid and a vapor product stream including acetic acid, methyl iodide, methyl acetate and water; condensing a first portion of the steam product stream to form a liquid stream and a steam stream; feeding a second portion of the steam product stream to a first column; feeding part or all of the liquid stream to the first column; and extracting a side stream comprising an acetic acid product from the first column, wherein the liquid stream is fed to the first column above the feed of the second portion of the steam product stream and in the that the liquid stream is fed to the first column below the point where the side stream comprising the acetic acid product is withdrawn from the first column. Without being limited by theory, the hydraulic load can be reduced in the first column above where the lateral current is withdrawn. Advantageously, this increases the production rates of the process.

The process for producing acetic acid according to some aspects of the present disclosure comprises carbonylation of at least one reagent selected from the group consisting of methanol, dimethyl ether, methyl acetate and mixtures thereof in the presence of water from 0.1 to 14% by weight, a metal catalyst, methyl iodide, and iodide salt to form a reaction medium in a reactor, separate the reaction medium into a recycled liquid, and a vapor product stream including acetic acid, iodide from methyl, methyl acetate, and water in a flash tank that has an optional top wash section, condense a first portion of the steam product stream to form a liquid product stream and a steam stream, feed a second portion from the steam product stream to a first column, extract a side stream comprising an acetic acid product from the first column column to a second column, feed part of the liquid product stream to the second column and obtain a purified acetic acid product from the second column. Optionally, due to entrainment of catalyst and other corrosive metals, the flash can have a scrubber section. Advantageously, this increases the production rates of the process.

In this regard, the liquid stream is divided and fed to the first and second columns. Preferably, the amount of liquid stream being divided is greater than the amount of liquid stream, if any, that is recycled to the reactor.

The vapor product stream from the flash vaporizer comprises acetic acid, methyl iodide, methyl acetate, water, and other impurities such as acetaldehyde, crotonaldehyde, higher acetates, and organic iodides. The concentration of acetic acid in the steam product stream can vary from 30 to 70% by weight, for example, from 40 to 60% by weight or from 45 to 55% by weight. The steam product stream normally transfers latent heat from the reaction to the first column to recover acetic acid in the side stream. The latent heat of the reaction may exceed the energy requirements of the first column, and thus the embodiments according to the present disclosure advantageously condense a first portion of the steam product stream to recover an acid enriched liquid stream acetic. The remaining portion of the steam product, i.e. the second portion, is introduced into the first column to further remove impurities and components from the reaction medium. The amount of the vapor product stream that is condensed may be a sufficient amount that does not affect the energy requirements of the first column. In condensation of the steam product stream, the liquid stream can be enriched in acetic acid compared to the steam product stream. In one embodiment, the acetic acid composition in the liquid stream relative to the acetic acid composition in the vapor product stream is enriched by at least 5%, for example, at least 10% or at least fifteen %. The concentration of acetic acid in the liquid stream can be from 65 to 95% by weight acetic acid, for example from 70 to 90% by weight acetic acid or from 80 to 90% by weight acetic acid.

Condensation from the liquid stream can remove reactive components and impurities in a vapor stream. The steam stream can be sent to a washing tower or an impurity removal column to recover the reactive components and, in particular, methyl iodide and methyl acetate. In other embodiments, the steam stream or a portion thereof can be purged as needed.

Once cooled, at least 10% of the liquid stream can be fed to the first column and / or the second column. In a preferred embodiment, at least 25%, for example, at least 50%, at least 75% or at least 90%, of the liquid stream can be fed to the first column and / or the second column. When introduced into the first column, the liquid stream is introduced above the feed of the second portion of the steam product stream and below the side stream. When introduced into the second column, the liquid stream can be introduced with the side stream feed or into the upper portion of the second column. Although the location is not particularly limited, it is preferable that the liquid stream enters the first and / or the second column in a location that does not interrupt the dynamics of the column. As more liquid stream is fed into the first and / or second column, less acetic acid is recycled to the reactor. As described in the US Publication. No. 2013/0116470, the liquid stream is fed into the reactor for cooling purposes. A disadvantage of this is that acetic acid is recycled and carbon monoxide efficiency decreases because recycling of the liquid stream leads to increased flow of the stream from the reactor to the flash vaporizer containing dissolved and entrained gases, which They mainly contain carbon monoxide. The dissolved and entrained gases are subsequently lost in the purification train vents. Furthermore, by returning a large liquid stream containing acetic acid, the liquid stream would need to increase in pressure in order to be fed to the reactor. Recycling of acetic acid increases recycles to the reactor and additional pumping would be required, affecting both equipment and operating costs. This imposes additional limitations on the use of the liquid stream as a coolant for the reactor. In one embodiment, all of the liquid stream is fed to the first and / or second column and none of the liquid stream is returned to the reactor. In such an embodiment, the reactor may have a separate cooling system and does not require the input of recycling steps to cool the reactor. By avoiding the need to recycle the liquid stream to the reactor, in embodiments, the process can maintain carbon monoxide efficiencies of over 90%, defined as the amount of carbon monoxide feed that is converted to acetic acid.

Embodiments will now be described in detail with reference to the drawings. The embodiments shown in FIG. 1 and 2 show a process for producing a purified acetic acid product from a liquid medium generated by a continuous carbonylation reaction of a methanol reagent in the presence of the metal catalyst, methyl iodide, water, and a salt of iodide.

Reaction stage

The example reaction and acetic acid recovery system 100 are shown in FIGS. 1 and 2. As shown, the methanol containing feed stream 101 and the carbon monoxide containing feed stream 102 are directed to the liquid phase carbonylation reactor 105, where the carbonylation reaction occurs to form acid acetic.

The methanol-containing feed stream 101 may comprise at least one member selected from the group consisting of methanol, dimethyl ether, and methyl acetate. The methanol-containing feed stream 101 may be derived in part from a fresh feed or may be recycled from the system. At least part of the methanol and / or reactive derivative thereof will be converted and, therefore, presented as methyl acetate in the liquid medium by esterification reaction with acetic acid.

Normal reaction temperatures for carbonylation will be 150 to 250 ° C, with the temperature range 180 to 225 ° C being a preferred range. The partial pressure of carbon monoxide in the reactor can vary widely, but is typically 0.20 to 3.04 MPa (2 to 30 atm), for example, 0.30 to 1.01 MPa (3 to 10 atm). The hydrogen partial pressure in the reactor is typically 0.0051 to 0.20 MPa (0.05 to 2 atm), for example 0.10 to 0.19 MPa (1 to 1.9 atm) . Due to the partial pressure of the by-products and the vapor pressure of the liquids contained, the total pressure of the reactor will vary between 1.52 and 4.05 MPa (15 and 40 atm). The production rate of acetic acid can be from 5 to 50 mol / lh, for example, from 10 to 40 mol / lh and preferably from approximately 15 to 35 mol / lh.

The carbonylation reactor 105 is preferably a stirred vessel or a bubble column type vessel, with or without a stirrer, within which the contents of the reactive liquid or suspension are maintained, preferably automatically, at a predetermined level, which preferably remains substantially constant during normal operation. In the carbonylation reactor 105, fresh methanol, carbon monoxide and enough water are continuously introduced as necessary to maintain adequate concentrations in the reaction medium.

The metal catalyst may comprise a Group VIII metal. Suitable Group VIII catalysts include rhodium and / or iridium catalysts. When a rhodium catalyst is used, the rhodium catalyst can be added in any suitable form so that the rhodium is in the catalyst solution as an equilibrium mixture including the anion [Rh (CO) ² I ² ] -, as it is well known in the art. The iodide salts optionally maintained in the reaction mixtures of the processes described herein can be in the form of a soluble salt of an alkali or alkaline earth metal, quaternary ammonium, phosphonium salt, or mixtures thereof. In certain embodiments, the catalyst co-promoter is lithium iodide, lithium acetate, or mixtures thereof. The salt co-promoter can be added as a salt without iodide which will generate an iodide salt. The iodide catalyst stabilizer can be directly introduced into the reaction system. Alternatively, the iodide salt can be generated in situ since under the operating conditions of the reaction system, a wide range of iodide-free salt precursors will react with methyl iodide or hydroiodic acid in the reaction medium to generate the stabilizer of Corresponding co-promoter iodide salt. For additional details regarding rhodium catalysis and iodide salt generation, see US Pat. No. 5,001,259; 5,026,908; 5,144,068 and 7,005,541. Carbonylation of methanol using iridium catalyst is well known and is generally described in US Pat. Nos. 5,942,460, 5,932,764, 5,883,295, 5,877,348, 5,877,347 and 5,696,284.

The halogen-containing catalyst promoter of the catalyst system consists of a halogen compound comprising an organic halide. Therefore, alkyl, aryl, and substituted alkyl or aryl halides can be used. Preferably, the halogen-containing catalyst promoter is present in the form of an alkyl halide. Even more preferably, the halogen-containing catalyst promoter is present in the form of an alkyl halide in which the alkyl radical corresponds to the alkyl radical of the feed alcohol, which is being carbonylated. Therefore, in the carbonylation of methanol to acetic acid, the halide promoter will include methyl halide and more preferably methyl iodide.

The components of the reaction medium are kept within defined limits to ensure sufficient production of acetic acid. The reaction medium contains a concentration of the metal catalyst, for example, rhodium catalyst, in an amount of 200 to 3000 ppmp, for example, 800 to 3000 ppmp, or 900 to 1500 ppmp. The concentration of water in the reaction medium is maintained up to 14% by weight, for example, from 0.1% by weight to 14% by weight, from 0.2% by weight to 10% by weight or from 0.25% by weight to 5% by weight. Preferably the reaction is carried out under low water conditions and the reaction medium contains 0.1 to 4.1% by weight water, for example 0.1 to 3.1% by weight or 0.5 to 2.8% by weight. The concentration of methyl iodide in the reaction medium is maintained from 1 to 25% by weight, for example, from 5 to 20% by weight, from 4 to 13.9% in weight. The concentration of iodide salt, for example lithium iodide, in the reaction medium is maintained from 1 to 25% by weight, for example, from 2 to 20% by weight, from 3 to 20% by weight. The concentration of methyl acetate in the reaction medium is maintained from 0.5 to 30% by weight, for example, from 0.3 to 20% by weight, from 0.6 to 4.1% by weight. The following amounts are based on the total weight of the reaction medium. The ranges disclosed in the present application include endpoints, sub-ranges, and individual values.

The concentration of acetic acid in the reaction medium is generally more than 30% by weight, for example, more than 40% by weight or more than 50% by weight.

In some embodiments, the desired reaction rates are obtained even at low concentrations of water by maintaining in the reaction medium an ester of the desired carboxylic acid and an alcohol, desirably the alcohol used in the carbonylation and an additional iodide ion above and above the iodide ion that is present as hydrogen iodide. A desired ester is methyl acetate. The additional iodide ion is desirably a salt of iodide, with lithium iodide (LiI) being preferred. It has been found that, as described in US Pat. No. 5,001,259, with low concentrations of water, methyl acetate and lithium iodide act as velocity promoters only when relatively high concentrations of each of these components are present and that promotion is greatest when both components are present simultaneously .

The carbonylation reaction of the methanol product to acetic acid can be performed by contacting the methanol feed with gaseous carbon monoxide through an acetic acid solvent reaction medium containing the rhodium catalyst, methyl iodide promoter, methyl acetate and additional soluble iodide salt, under suitable temperature and pressure conditions to form the carbonylation product. It will be generally recognized that what is important is the concentration of iodide ion in the catalyst system and not the cation associated with iodide, and that at a given molar concentration of iodide, the nature of the cation is not as significant as the effect of the concentration iodide. Any metal iodide salt, or any iodide salt of any organic cation, or other cations such as those based on amine or phosphine compounds (optionally, ternary or quaternary cations), can be maintained in the reaction medium provided that the salt is sufficiently soluble in the reaction medium to provide the desired level of iodide. When iodide is a metal salt, it is preferably a iodide salt of a member of the group consisting of the Group IA and Group IIA metals of the periodic table as set forth in the "Handbook of Chemistry and Physics" published by CRC Press, Cleveland, Ohio, 2002-03 (83rd edition). In particular, alkali metal iodides are useful, with lithium iodide being particularly suitable. In the low water carbonylation process, the additional iodide ion above and below the iodide ion present as hydrogen iodide is generally present in the catalyst solution in amounts such that the total concentration of iodide ions is 1 25 wt% and methyl acetate is generally present in amounts of 0.5 to 30 wt% and methyl iodide is generally present in amounts of 1 to 25 wt%. The rhodium catalyst is generally present in amounts of 200 to 3000 ppmp.

To control the exothermic carbonylation reaction, the reactor may have a sufficient cooling system. This reduces the need to recycle the liquid stream to provide the necessary cooling for the reactor. In one embodiment, there may be a pumping circuit 103 to cool the reactor. Pumping circuit 103 operates to cool the reaction medium by indirect contact with a coolant. Suitable pumping circuits are described in US Pat. No. 8,530,696. In one embodiment, the steam generator can recover heat from the reaction in pumping reactor 103.

In a typical carbonylation process, carbon monoxide is continuously introduced into the carbonylation reactor, desirably below the stirrer, which can be used to stir the contents. The gaseous feed is preferably dispersed through the reaction liquid by this stirring means. Desirably, the gas purge stream 106 is vented from reactor 105 to prevent accumulation of gas by-products and to maintain a partial pressure of carbon monoxide at a given total reactor pressure. The reactor temperature can be controlled and the carbon monoxide feed is introduced at a rate sufficient to maintain the desired total reactor pressure. Stream 113 comprising the liquid reaction medium exits reactor 105.

The acetic acid production system preferably includes separation system 108 used to recover acetic acid and recycle metal catalyst, methyl iodide, methyl acetate and other system components within the process. One or more of the recycle streams can be combined before being introduced into the reactor. The separation system also preferably controls the water and acetic acid content in the carbonylation reactor, as well as throughout the system, and facilitates removal of the permanganate reducing compound ("PRC"). PRCs can include acetaldehyde, acetone, methyl ethyl ketone, butylaldehyde, crotonaldehyde, 2-ethyl crotonaldehyde, 2-ethyl butyraldehyde, and the aldolic condensation products thereof.

The reaction medium is withdrawn from the carbonylation reactor 105 at a rate sufficient to maintain a constant level therein, and is provided to the flash vaporizer 110 through stream 113. The flash separation can be performed at a temperature of 80 ° C to 200 ° C, with an absolute pressure of 0.10 to 1.01 MPa (from 1 to 10 atm). The reaction medium is separated in an instantaneous separation stage to obtain a flow of steam product 112 comprising acetic acid and liquid recycling 111 comprising a solution containing catalyst. The catalyst-containing solution may be predominantly rhodium-containing acetic acid and the iodide salt together with lower amounts of methyl acetate, methyl iodide and water and recycled to the reactor, as discussed above. Before returning the liquid recycle to the reactor, a side stream can pass through a corrosion metal removal bed, such as an ion exchange bed, to remove any entrained corrosion metal as described in US Patent No. .UU. No. 5,731,252. Furthermore, the corrosion metal removal bed can be used to remove nitrogen compounds, such as amines, as written in US Pat. No. 8,697,908.

In addition to acetic acid, the vapor product stream 112 also comprises methyl iodide, methyl acetate, water, PRC, and other iodide compounds. The dissolved gases leaving reactor 105 and entering flash vaporizer 110 comprise a portion of the carbon monoxide and may also contain gaseous by-products such as methane, hydrogen and carbon dioxide. Said dissolved gases exit the flash vaporizer 110 as part of the vapor product stream 112. In one embodiment, carbon monoxide can be fed in gas purge stream 106 to the base of flash vaporizer 110 to enhance the stability of the rhodium.

Condensation of the steam product stream

As shown in FIG. 1 and 2, the steam product stream 112 is divided into a first portion 140 and a second portion 141. These portions are aliquots of the steam product stream. The first portion 140 is condensed by the heat exchanger 142 to form a liquid stream 143 and a steam stream 144.

In one embodiment, the steam product stream 112 condensing as the first portion 140 may be 1 to 50% of the steam product stream 112, for example, preferably 5 to 40% or more preferably 10 to 35%. The first portion 140 is cooled with a heat exchanger 142 to a temperature of from 20 ° C to 100 ° C, for example, from 20 ° C to 70 ° C or more preferably from 20 ° C to 50 ° C.

The steam product stream 112 which is not condensed and fed to the first column 120 as the second portion 141 may be 50 to 99% of the steam product stream, eg preferably 60 to 95% or more preferably 65 to 90%.

As shown in FIG. 1, once cooled, at least 10% of the liquid stream 143 can be fed to the first column 120. In a preferred embodiment, at least 25%, for example, at least 50%, at least 75% or at least 90% can be fed to the first column 120. The remaining portion of the liquid stream 143 not fed to the first column 120 can preferably be fed to the second column 125 or less preferably can be fed to the reactor 105 through the Optional line 145. To avoid recycling acetic acid to reactor 105, more acetic acid from liquid stream 143 can be fed to first column 120 and / or second column 125 than is returned to reactor 105. To reduce hydraulic head in the first column 120, the entire portion of the liquid stream 143 is introduced above the feed from the second portion 141 to the first column 120. As indicated in FIG. 1, liquid stream 143 is fed to first column 120 at a point above 141 and below side stream 124 to prevent entrainment of components present in liquid stream 143 into side stream 124. In particular, the rhodium catalyst entrained in the vapor product stream 112 is prevented from entraining in the side stream 124 by locating the liquid stream 143 below the level at which the side stream 124 is withdrawn from the first column 120.

In another embodiment, as shown in FIG. 2, once cooled, at least 10% of the liquid stream 143 can be fed to the second column 125. In a preferred embodiment, at least 25%, for example, at least 50%, at least 75% or at least 90% can be fed to the second column 125. Because there may be low levels of entrained catalysts in the steam product stream 112 and because the first column 120 may be skipped, it is desirable to remove the entrained catalyst earlier. for the vapor product stream 112 to exit the instant vaporizer 110. In FIG. 2, to avoid sending entrained metal catalyst to the second column 125, a wash tower section 150 is provided in the upper portion of the flash vaporizer 110. A wash 151 can be added to the wash tower section 150 to remove the entrained metals. In embodiments, wash 151 may comprise one or more of streams 133, 136 and high boiling residue stream 121. Accordingly, in embodiments, the process further comprises directing a bottom stream from the first column, a bottom stream from the second column, a head product stream from the second column, or a combination thereof, in the upper washing tower section in an amount sufficient to remove at least a portion of the catalyst entrained in the steam product stream. In embodiments, the wash flow 151 sufficient to remove at least a portion of the entrained catalyst in the steam product stream is 1% by weight to 50% by weight of the steam product stream 112.

The remaining portion of the liquid stream 143 not fed to the second column 125 is fed to the first column 120. It is important to note that, in embodiments, the remaining portion of the liquid stream 143 is not it feeds a head product decanter or other container associated with stream 133. Stream 143 includes a substantial amount of acetic acid. As described herein, stream 133 can be biphasic separated into a light aqueous phase and a heavy methyl iodide phase prior to purification and further removal of PRCs. The acetic acid present in stream 143 can affect the phase separation of stream 133 and thus have a detrimental effect on the process.

Acetic acid recovery

The distillation and recovery of acetic acid is not particularly limited for the purposes of the present disclosure. Unlike previous methods that recover acetic acid from the steam product stream, the processes disclosed herein recover acetic acid from both the steam product stream and a condensed liquid stream from the product stream vapor that is enriched in acetic acid.

As shown in FIG. 1, the second portion 141 of the steam product stream 112 refers to a first column 120, also called a light end product column, together with part or all of the liquid stream 143. The distillation produces a steam stream of low boiling point head product 122, a purified acetic acid product which is preferably removed through a side stream 124 and a high boiling point residue stream 121. In one embodiment, the low boiling point overhead product vapor stream 122 may comprise 40 to 80 wt% water, methyl acetate, methyl iodide and carbonyl impurities. Side stream 124 may comprise 90 to 98 wt% acetic acid, 1 to 2.5 wt% water, 0.1 to 5 wt% methyl iodide and 0.1 to 5% methyl acetate in weigh. The acetic acid withdrawn through side stream 124 is preferably subjected to further purification, such as in a second column 125, also called a drying column, and separates side stream 124 into overhead product stream 126 consisting primarily of water and bottom stream 127 composed primarily of acetic acid. The overhead product stream 126 may comprise 50 to 75 wt% water. Methyl acetate and methyl iodide are also removed from the side stream and concentrated in the overhead product stream. The drying column bottom stream 127 preferably comprises or consists essentially of acetic acid. In preferred embodiments, the drying column bottom stream 127 comprises acetic acid in an amount of greater than 90% by weight, eg, greater than 95% by weight or greater than 98% by weight. The drying column bottom stream 127 can be further processed, for example, by passing it through an ion exchange resin, before storing or transporting it for commercial use.

As shown in FIG. 2, the second vapor product stream portion 141 is directed to the first column 120. The distillation produces a low boiling point overhead product vapor stream 122, a side stream 124 comprising acetic acid and a stream residue 121 of high boiling point. Side stream 124 is subjected to further purification, along with some or all of liquid stream 143, in second column 125. Second column 125 functions to separate side stream 124 and liquid stream 143 in stream overhead product 126 composed mainly of water and bottom stream 127 composed mainly of acetic acid. In one embodiment, due to the enriched acetic acid concentration of the liquid stream 143, compared to the vapor product stream 112, the liquid stream 143 can be separated in the second column without interrupting the dynamics of the column. Advantageously, an acetic acid product having the same purity can be recovered when the liquid stream 143 is fed to the second column 125.

In embodiments, the vapor product stream 112 comprises acetic acid, methyl iodide, methyl acetate, water, acetaldehyde, and hydrogen iodide. In embodiments, the vapor product stream 112 comprises acetic acid in an amount of 45 to 75% by weight, methyl iodide in an amount of 20 to 50% by weight, methyl acetate in an amount less than or equal to 9% by weight and water in an amount less than or equal to 15% by weight, based on the total weight of the steam product stream. In other embodiments, the vapor product stream 112 comprises acetic acid in an amount of 45 to 75% by weight, methyl iodide in an amount of 24 to less than 36% by weight, methyl acetate in an amount less than or equal to 9% by weight and water in an amount less than or equal to 15% by weight, based on the total weight of the steam product stream. In embodiments, the vapor product stream 112 comprises acetic acid in an amount of 55 to 75% by weight, methyl iodide in an amount of 24 to 35% by weight, methyl acetate in an amount of 0.5 to 8 % by weight and water in an amount of 0.5 to 14% by weight. In still other embodiments, the vapor product stream 112 comprises acetic acid in an amount of 60 to 70% by weight, methyl iodide in an amount of 25 to 35% by weight, methyl acetate in an amount of 0.5 6.5% by weight and water in an amount of 1 to 8% by weight. The concentration of acetaldehyde in the steam product stream can be in an amount of 0.005 to 1% by weight, based on the total weight of the steam product stream, for example 0.01 to 0.8% in weight or from 0.01 to 0.7% by weight. In some embodiments, acetaldehyde may be present in amounts less than or equal to 0.01% by weight. Steam product stream 112 may comprise hydrogen iodide in an amount of less than or equal to 1% by weight, based on the total weight of the steam product stream, for example, less than or equal to 0.5% by weight or less than or equal to 0.1% by weight. The steam product stream 112 is preferably substantially free, that is, it contains an amount less than or equal to 0.0001% by weight, of propionic acid, based on the total weight of the steam product stream.

However, as discussed above, vapor stream 112 can also include a substantial amount of rhodium catalyst through entrainment during instantaneous vaporization in instantaneous vaporizer 110. Catalyst entrainment represents a significant cost due to the associated expense to the rhodium catalyst. In addition, entrainment of rhodium can cause blockages and other downstream problems, as well as result in measurable concentrations of rhodium in the final acetic acid product. Consequently, the wash tower 150 and / or the proper location of the liquid stream 143 with respect to the steam stream 141 and the side draw stream 124 result in an unexpected improvement in the art.

Liquid recycle stream 111 comprises acetic acid, metal catalyst, corrosion metals, as well as various other compounds. In one embodiment, the liquid recycle stream comprises acetic acid in an amount of 60 to 90% by weight, metal catalyst in an amount of 0.01 to 0.5% by weight; Corrosion metals (eg, nickel, iron, and chromium) in a total amount of 10 to 2,500 ppmp; lithium iodide in an amount of 5 to 20% by weight; methyl iodide in an amount of 0.5 to 5% by weight; methyl acetate in an amount of 0.1 to 5% by weight; water in an amount of 0.1 to 8% by weight; acetaldehyde in an amount less than or equal to 1% by weight (for example, acetaldehyde from 0.0001 to 1% by weight); and hydrogen iodide in an amount less than or equal to 0.5% by weight (for example, hydrogen iodide from 0.0001 to 0.5% by weight).

The low boiling point overhead product vapor stream 122 separated from the first column 120 contains a reaction component, such as methyl iodide, methyl acetate and water, and it is preferable to retain these reaction components within the process. The low boiling point overhead product vapor stream 122 is condensed by a heat exchanger in stream 133, which can be recycled to reactor 105 and / or reflux to first column 120. An exhaust gas component can be vented through line 132 from condensed low boiling point head product vapor stream 124. In addition, there may be a procedure for removing carbonyl impurities, such as acetaldehyde, that deteriorate the quality of the acetic acid product and can be removed in suitable impurity removal columns, extractors, and absorbents as described in US Patents. . No. 6,143,930; 6,339,171; 7,223,883; 7,223,886; 7,884,237; 7,855,306; and the US Publications No. 2006/0011462 and 2011/0288333. Carbonyl impurities, such as acetaldehyde, can react with iodide catalyst promoters to form alkyl iodides, for example, ethyl iodide, propyl iodide, butyl iodide, pentyl iodide, hexyl iodide, etc. Furthermore, because many impurities are originated with acetaldehyde, it is desirable to remove acetaldehyde from the low boiling condensed overhead product vapor stream in stream 133 before returning the stream to the reactor. These impurities may also be referred to herein as PRC, which are described herein.

Although not shown, a portion of stream 133 can be condensed and separated biphasically into a light aqueous liquid phase and / or a heavy liquid phase composed primarily of methyl iodide, and then directed to an acetaldehyde or PRC removal system to recover methyl iodide and methyl acetate, while removing acetaldehyde. As shown in Tables 1 and 2, the light liquid phase and / or the heavy liquid phase separated from stream 133 may each contain a PRC and the process may include removal of carbonyl impurities, such as acetaldehyde, that deteriorate the acetic acid product quality and can be removed in suitable columns and impurity removal absorbers as described in US Pat. No. 6,143,930; 6,339,171; 7,223,883; 7,223,886; 7,855,306; 7,884,237; 8,889,904; and the US Publication No. 2006/0011462. Carbonyl impurities, such as acetaldehyde, can react with iodide catalyst promoters to form alkyl iodides, for example, ethyl iodide, propyl iodide, butyl iodide, pentyl iodide, hexyl iodide, etc. Furthermore, because many impurities are originated with acetaldehyde, it is desirable to remove carbonyl impurities from the liquid light phase.

The portion of stream 133, i.e. the light aqueous phase and / or the heavy liquid phase fed to the acetaldehyde removal system or PRC may vary from 1% to 99% of the mass flow of the light liquid phase and / or the heavy liquid phase, for example from 1 to 50%, from 2 to 45%, from 5 to 40%. 5 to 30% or 5 to 20%. Also in some embodiments, a portion of both the light liquid phase and the heavy liquid phase can be fed to the acetaldehyde removal system or PRC. The portion of the light liquid phase not fed to the acetaldehyde or PRC removal system can either reflux to the first column 120 or be recycled to reactor 105, as described herein. The portion of the heavy liquid phase that is not fed to the acetaldehyde or PRC removal system can be recycled to reactor 105. Although a portion of the heavy liquid phase can flow back to the first column, it is more desirable to return the iodide enriched liquid phase of methyl to the reactor.

Although the specific compositions of the light liquid phase can vary widely, some example compositions are provided below in Table 1.

TABLE 1

Example light liquid phase of head product of final products _______________________________ light ______________________________ Conc. Component (wt%) conc. (wt%) conc. (% in weigh)

Water 40-80 50-75 70-75

Methyl Acetate 1-50 1-25 1-15

Acetic acid 1-40 1-25 5-15

PRC <5 <3 <1

Methyl iodide <10 <5 <3

In embodiments, a top product decanter from the first column 120 is arranged and constructed to maintain a low interface level to avoid excessive retention of methyl iodide. Although the specific compositions of the heavy liquid phase can vary widely, some example compositions are provided below in Table 2.

TABLE 2

Heavy liquid phase of light end product head product example

Component conc. (wt%) conc. (wt%) conc. (% in weigh)

Water 0.01-2 0.05-1 0.1-0.9

Methyl acetate 0.1-25 0.5-20 0.7-15

Acetic acid 0.1-10 0.2-8 0.5-6

PRC <5 <3 <1

Methyl Iodide 40-98 50-95 60-85

Distillation columns and other containers suitable for use include conventional distillation columns, for example, a plate column, a compact column, and others. Plate columns may include a perforated plate column, a gurgling bell column, a Kittel tray column, a single-flow tray, or a corrugated tray column. The material of the distillation column is not limited and may include glass, metal, ceramic, or other suitable material may be used. For a plate column, the theoretical number of plates is not particularly limited and, depending on the species of the component to be separated, may depend on the component to be separated and may include up to 5080 plates, for example from 2 to 80, 5 to 60, 5 to 50, or more preferably 7 to 35. The distillation column may include a combination of different distillation apparatus. For example, a combination of bubbling bell column and perforated plate column can be used, as well as a combination of perforated plate column and a compacted column.

The distillation temperature and pressure in the distillation system can be appropriately selected depending on conditions such as the species of the target carboxylic acid and the species of the distillation column, or the removal target selected from the lowest boiling point impurity and the highest boiling point impurity according to the composition of the feed stream. For example, in a case where the distillation column performs purification of acetic acid, the internal pressure of the distillation column (usually the pressure at the top of the column) may be 0.01 to 1 MPa, for example 0.02 to 0.7 MPa, and more preferably 0.05 to 0.5 MPa in terms of gauge pressure. Furthermore, the distillation temperature for the distillation column, that is, the internal temperature of the column at the temperature of the top of the column, can be controlled by adjusting the internal pressure of the column and, for example, can be 20 at 200 ° C, for example from 50 to 180 ° C and, more preferably, from about 100 to 160 ° C.

The material of each member or unit associated with the distillation system, including the columns, valves, condensers, receivers, pumps, boilers and internals, and various pipes, each communicating with the distillation system, may be a suitable material, such as glass , metal, ceramic or combinations thereof, and is not limited in particular to a specific one. In embodiments, the material of the above distillation system and various pipes is a transition metal or a transition metal-based alloy, such as an iron alloy, for example, stainless steel, nickel, or nickel, zirconium, or zirconium thereof, titanium or titanium alloy thereof or aluminum alloy. A suitable iron-based alloy includes any alloy that contains iron as the main component, for example, a stainless steel that also comprises chromium, nickel, molybdenum, and others. A suitable nickel-based alloy includes containing nickel as the main component and one or more of chromium, iron, cobalt, molybdenum, tungsten, manganese and others, eg HASTELLOY ™ and INCONEL ™. Corrosion resistant metals may be particularly suitable as materials for the distillation system and various pipelines.

In one embodiment, a portion of the light liquid phase and / or heavy liquid phase is fed to a distillation column that enriches the overhead product thereof to have acetaldehyde and methyl iodide. Depending on the configuration, there may be two separate distillation columns, and the top product of the second column may be enriched in acetaldehyde and methyl iodide. Dimethyl ether, which can be formed in situ, may also be present in the overhead product. The overhead product may undergo one or more extraction steps to remove a raffinate enriched in methyl iodide and an extractor. A portion of the refined can be returned to the distillation column, the first column, the overhead product decanter and / or the reactor. For example, when the heavy liquid phase is treated in the PRC removal system, it may be desirable to return a portion of the raffinate to the distillation column or reactor. In addition, for example, when treating the light liquid phase in the PRC removal system, it may be desirable to return a portion of the raffinate to the first column, the overhead product decanter, or the reactor. In some embodiments, the extractor can be further distilled to remove water, which is returned to the one or more extraction stages where it contains more methyl acetate and methyl iodide than the light liquid phase, it can also be recycled to reactor 105 and / or or reflow to first column 120.

Accordingly, the low boiling point product vapor stream condensed in stream 133 can be separated into an aqueous phase and an organic phase, and these phases can be recycled or refluxed as necessary to maintain concentrations in the medium. reaction. Furthermore, carbonyl impurities can be removed from these phases.

Similarly, the overhead product stream 126 from second column 125 contains a reaction component, such as methyl iodide, methyl acetate, and water, and it is preferable to retain these reaction components within the process. The overhead product stream 126 is condensed by a heat exchanger in stream 136, which is recycled to reactor 105 and / or back to second column 125. An exhaust gas component can be vented through line 135 from of the low boiling point condensed product vapor stream 126. Similar to the condensed low boiling point head product vapor stream in stream 133, the condensed head product stream in stream 136 can also be separated into an aqueous phase and an organic phase, and these phases can be recycled or Reflux as necessary to maintain concentrations in the reaction medium.

To recover components, especially reaction components, from the ventilation stream, in particular pipes 106, 132, 135 and 144, these pipes can be fed to a washing tower that runs on methanol and / or chilled acetic acid to recover acetate of methyl and methyl iodide that can be recycled directly or indirectly to the reactor. A suitable washing tower is described in US Pat. No. 8,318,977.

The distillation columns according to the present disclosure can be a conventional distillation column, for example a plate column, a compact column, and others. The material of the distillation column is not limited and may include glass, metal, ceramic, or other suitable material may be used. For a plate column, the theoretical number of plates can depend on the component to be separated and can include up to 50 plates, for example from 5 to 50 or from 7 to 35. Protective bed

Carboxylic acid streams, eg, acetic acid streams that are contaminated with halides and / or corrosive metals can be contacted with the ion exchange resin composition of the invention under a wide range of operating conditions. Preferably, the ion exchange resin composition is provided in a protective bed. The use of buffer beds to purify contaminated carboxylic acid streams is well documented in the art, for example, US Pat. No. 4,615,806; 5,653,853; 5,731,252; and 6,225,498. Generally, a stream of contaminated liquid carboxylic acid is contacted with the ion exchange resin composition, which is preferably disposed in the protective bed. Halide contaminants, for example, iodide contaminants, react with metal to form metal iodides. In some embodiments, hydrocarbon moieties, eg, methyl groups, that may be associated with iodide can esterify carboxylic acid. For example, in the case of acetic acid contaminated with methyl iodide, methyl acetate would be produced as a by-product of iodide removal. The formation of this esterification product does not normally have a detrimental effect on the treated carboxylic acid stream.

The pressure during the contact stage is limited only by the physical resistance of the resin. In one embodiment, contact is made at pressures ranging from 0.1 MPa to 1 MPa, for example, from 0.1 MPa to 0.8 MPa or from 0.1 MPa to 0.5 MPa. For convenience, however, both pressure and temperature can preferably be set such that the contaminated carboxylic acid stream is processed as a liquid. Thus, for example, when operated at atmospheric pressure, which is generally preferred based on economic considerations, the temperature can range from 17 ° C (the freezing point of acetic acid) to 118 ° C (the boiling point of acetic acid). It is within the scope of those skilled in the art to determine analogous ranges for product streams comprising other carboxylic acid compounds. The temperature of the contact stage is preferably kept relatively low to minimize degradation of the resin. In one embodiment, the contact is made at a temperature ranging from 25 ° C to 120 ° C, for example, from 25 ° C to 100 ° C or from 50 ° C to 100 ° C. Some cationic macroreticular resins normally begin to degrade (via the acid catalyzed aromatic desulfonation mechanism) at temperatures of 150 ° C. Carboxylic acids having up to 5 carbon atoms, for example up to 3 carbon atoms, remain liquid at these temperatures. Therefore, the temperature during contact must be kept below the degradation temperature of the resin used. In some embodiments, the operating temperature is kept below the resin temperature limit, consistent with liquid phase operation and the desired kinetics for halide removal.

The configuration of the protective bed within an acetic acid purification train can vary widely. For example, the protective bed can be configured after a drying column. Additionally, or as Alternatively, the protection can be configured after a heavy end product removal column or a finishing column. Preferably, the protective bed is configured in a position where the temperature of the acetic acid product stream is low, for example, less than 120 ° C or less than 100 ° C. In addition to the benefits discussed above, lower temperature operation provides less corrosion compared to higher temperature operation. Operating at a lower temperature provides less formation of corrosive metal contaminants, which, as discussed above, can decrease the overall life of the resin. Furthermore, because lower operating temperatures result in less corrosion, the containers advantageously do not need to be made of expensive corrosion resistant metals, and lower quality metals, eg, conventional stainless steel, can be used.

In one embodiment, the flow rate through the protective bed varies from 0.1 bed volumes per hour ("VL / h") to 50 VL / h, for example, from 1 VL / h to 20 VL / h or 6 VL / h has 10 VL / h. An organic medium bed volume is a volume of the medium equal to the volume occupied by the resin bed. A flow rate of 1 VL / h means that an amount of organic liquid equal to the volume occupied by the resin bed passes through the resin bed in a time period of one hour.

To avoid depleting the resin with a purified acetic acid product that is high in the total iodide concentration, in one embodiment, the purified acetic acid product in the bottom stream 127 is contacted with a protective bed when the concentration Total iodide of the purified acetic acid product is less than 1 ppmp. The total concentration of iodide includes iodide from both organic sources, C ¹ to C ¹⁴ alkyl iodides, and inorganic sources, such as hydrogen iodide. A purified acetic acid composition is obtained as a result of the protective bed treatment. The purified acetic acid composition, in one embodiment, comprises less than 100 ppbp, iodides, eg, less than 90 ppbp, less than 50 ppbp, or less than 25 ppbp. In one embodiment, the purified acetic acid composition comprises less than 100 ppbp of corrosive metals, eg, less than 750 ppbp, less than 500 ppbp, or less than 250 ppbp. In terms of ranges, the purified acetic acid composition can comprise from 0 to 100 ppbp of iodides, for example, from 1 to 50 ppbp; and / or from 0 to 1000 ppbp of corrosion metals, for example, from 1 to 500 ppbp. In other embodiments, the protective bed removes at least 25% by weight of the iodides from the crude acetic acid product, for example, at least 50% by weight or at least 75% by weight. In one embodiment, the protective bed removes at least 25% by weight of the corrosion metals from the crude acetic acid product, for example, at least 50% by weight or at least 75% by weight.

In embodiments, the process for producing acetic acid further includes introducing a lithium compound into the reactor to maintain the lithium acetate concentration in an amount of 0.3 to 0.7% by weight in the reaction medium. In embodiments, an amount of the lithium compound is introduced into the reactor to maintain the concentration of hydrogen iodide in an amount of 0.1 to 1.3% by weight in the reaction medium. In embodiments, the concentration of the rhodium catalyst is maintained in an amount of 300-3000 ppmp in the reaction medium, the concentration of water is maintained in an amount of 0.1 to 4.1% by weight in the reaction medium and the methyl acetate concentration is maintained from 0.6 to 4.1% by weight in the reaction medium, based on the total weight of the reaction medium present within the carbonylation reactor.

In embodiments, the lithium compound introduced into the reactor is selected from the group consisting of lithium acetate, lithium carboxylates, lithium carbonates, lithium hydroxide, other organic lithium salts, and mixtures thereof. In embodiments, the lithium compound is soluble in the reaction medium. In one embodiment, lithium acetate dihydrate can be used as the source of the lithium compound.

Lithium acetate reacts with hydrogen iodide according to the following equilibrium reaction (I) to form lithium iodide and acetic acid:

LiOAc HI 5 Lil HOAc (I)

Lithium acetate is believed to provide improved control of hydrogen iodide concentration relative to other acetates, such as methyl acetate, present in the reaction medium. Without being bound by theory, lithium acetate is a conjugate base of acetic acid and, therefore, is reactive against hydrogen iodide through an acid-base reaction. This property is believed to result in an equilibration of reaction (I) that favors reaction products over those produced by the corresponding equilibrium of methyl acetate and hydrogen iodide. This improved balance is favored by water concentrations of less than 4.1% by weight in the reaction medium. Furthermore, the relatively low volatility of lithium acetate compared to methyl acetate allows lithium acetate to remain in the reaction medium, except for volatility losses and small amounts of entrainment in the crude vapor product. In contrast, the relatively high volatility of methyl acetate allows the material to be distilled in the purification train, making methyl acetate more difficult to control. Lithium acetate is much easier to maintain and control in the process at uniform low concentrations of hydrogen iodide. Consequently, a relatively small amount of lithium acetate can be used relative to the amount of methyl acetate needed to control the concentrations of hydrogen iodide in the reaction medium. Lithium acetate has also been found to be at least three times more effective than methyl acetate in promoting the oxidative addition of iodide to methyl to rhodium complex [I].

In embodiments, the concentration of lithium acetate in the reaction medium is maintained greater than or equal to 0.3% by weight or greater than or equal to 0.35% by weight, or greater than or equal to 0.4% by weight, or greater than or equal to 0.45% by weight, or greater than or equal to 0.5% by weight, and / or in embodiments, the concentration of lithium acetate in the reaction medium is maintained less than or equal to 0, 7% by weight or less than or equal to 0.65% by weight, or less than or equal to 0.6% by weight, or less than or equal to 0.55% by weight, when determined according to acid titration Perchloric to a potentiometric end point.

It has been found that an excess of lithium acetate in the reaction medium can adversely affect the other compounds in the reaction medium, leading to a decrease in productivity. Conversely, a concentration of lithium acetate in the reaction medium below about 0.3 wt% has been found to result in a lack of control over the concentrations of hydrogen iodide within the reaction medium.

In embodiments, the lithium compound can be continuously or intermittently introduced into the reaction medium. In embodiments, the lithium compound is introduced during reactor startup. In embodiments, the lithium compound is intermittently introduced to replace carryover losses.

A series of experiments performed to demonstrate the promotional effect of lithium acetate in the carbonylation reactor and to determine the effect of lithium acetate on the oxidative addition of methyl iodide to the rhodium complex, Li [RhI ² (CO) ² ] confirmed the promotional effect of lithium acetate on reaction rates. A linear increase in reaction rates was observed correlated with the increase in lithium acetate concentrations. This correlation was indicative of the first-order promotional effects of the reaction between methyl iodide and Li [Rhh (CO) ² ]. These experiments further demonstrated a non-zero intersection, confirming that lithium acetate is not required for the MeI-Rh (I) reaction to occur, but lithium acetate produces a considerable promotional effect even at low concentrations.

In embodiments, the process may further comprise maintaining a concentration of butyl acetate in the acetic acid product at 10 ppmp or less without directly removing butyl acetate from the acetic acid product. In embodiments, the concentration of butyl acetate in the final acetic acid product can be kept below 10 ppm by removing acetaldehyde from the reaction medium, for example, removing acetaldehyde from a stream derived from the reaction medium, and / or controlling the temperature of reaction and / or the partial pressure of hydrogen, and / or the concentration of metal catalyst in the reaction medium. In embodiments, the concentration of butyl acetate in the final acetic acid product is maintained by controlling one or more of between the carbonylation reaction temperature of 150 ° C to 250 ° C, the hydrogen partial pressure in the carbonylation reactor of 0.03 to 0.20 MPa (0.3 to 2 atm), the rhodium metal catalyst concentration in the reaction medium of 100 to 3000 ppmp, based on the total weight of the reaction medium, and / or the concentration of acetaldehyde in the reaction medium at 1500 ppm or less.

In embodiments, the acetic acid product formed according to process embodiments disclosed herein has a butyl acetate concentration of less than or equal to 10 ppmp, or less than or equal to 9 ppmp, or less than or equal to 8 ppmp, or less than or equal to 6 ppmp, or less than or equal to 2 ppmp, based on the total weight of the acetic acid product. In embodiments, the acetic acid product is substantially free of butyl acetate, ie, a concentration of butyl acetate less than 0.05 ppmp or is not detectable by detection means known in the art. In embodiments, the acetic acid product may also have a propionic acid concentration of less than 250 ppmw or less than 225 ppm, or less than 200 ppmp.

In embodiments, the concentration of butyl acetate in the acetic acid product can be controlled by controlling the concentration of acetaldehyde in the reaction medium. Although not wishing to be bound by theory, butyl acetate is believed to be a by-product caused by aldol condensation of acetaldehyde. Applicant has found that by keeping the concentration of acetaldehyde in the reaction medium below 1500 ppmp, the concentration of butyl acetate in the final acetic acid product can be controlled below 10 ppmp. In embodiments, the concentration of acetaldehyde in the reaction medium is maintained less than or equal to 1500 ppmp or less than or equal to 900 ppmp, or less than or equal to 500 ppmp, or less than or equal to 400 ppmp, based on the total weight of the reaction medium.

In embodiments, the concentration of butyl acetate in the acetic acid product can be controlled by controlling the reaction temperature of the carbonylation reactor at a temperature greater than or equal to 150 ° C or 180 ° C and less than or equal to 250 ° C or 225 ° C; and / or the partial pressure of hydrogen in the carbonylation reactor can be controlled at more than or equal to 0.03 MPa (0.3 atm), or 0.035 MPa (0.35 atm), or 0.04 MPa (0, 4 atm), or 0.051 MPa (0.5 atm), and less than or equal to 0.2 MPa (2 atm), or 0.15 MPa (1.5 atm), or 0.10 MPa (1 atm) .

Although the relatively high hydrogen partial pressure results in improved reaction rates, selectivity, improved catalyst activity, and reduced temperatures, the Applicant has found that as the hydrogen partial pressure increases, the production of impurities, including acetate, also increases. from butyl.

In embodiments, the hydrogen partial pressure can be controlled by modifying the amount of hydrogen present in the carbon monoxide source and / or increasing or decreasing the reactor ventilation flows to obtain the desired hydrogen partial pressure within the carbonylation reactor.

A series of experiments was carried out to demonstrate the effect of the partial pressure of hydrogen and the concentration of acetaldehyde in the reaction medium on the concentration of butyl acetate in the final acetic acid product. These experiments confirmed a correlation between the reduced butyl acetate concentrations in the final acetic acid product and the relatively low acetaldehyde concentrations in the reaction medium and / or relatively low hydrogen partial pressures in the carbonylation reactor. Experiments in which the concentration of acetaldehyde in the reactor was kept below 1500 ppm and the hydrogen partial pressure of the reactor was kept below 0.061 MPa (0.6 atm) resulted in butyl acetate levels below 10 ppmp in the final acetic acid product. Other experiments demonstrated an acetaldehyde concentration in the reactor below 1500 ppmp and a reactor hydrogen partial pressure of 0.047 MPa (0.46 atm) resulted in a butyl acetate concentration of less than 8 ppmp in the product of final acetic acid. Similar conditions where the hydrogen partial pressure was 0.03 MPa (0.30 atm) resulted in butyl acetate levels below 6 ppmp, and hydrogen partial pressures of 0.061 MPa (0.60 atm) butyl acetate concentrations below 0.2 ppmp resulted in the final acetic acid product. However, comparative experiments in which the partial pressure of hydrogen was 0.4 and 0.3 respectively, but in the absence of an aldehyde removal system such that acetaldehyde concentrations in the reactor exceeded 1500 ppmp, gave as a result a final acetic acid product having butyl acetate levels of 13 ppmp and 16 ppmp respectively.

Applicant has further discovered that the concentration of propionic acid in the final acetic acid product can be affected by the concentration of butyl acetate in the acetic acid product. Consequently, by controlling the concentration of butyl acetate in the final acetic acid product at 10 ppmp or less, the concentration of propionic acid in the final acetic acid product can be controlled at less than 250 ppmp, or less than 225 ppmp, or less than 200 ppmp. Similarly, by controlling the ethanol content in the reactor feed, which may be present as an impurity in the methanol source, the concentrations of propionic acid and butyl acetate in the final acetic acid product can also be controlled. In embodiments, the concentration of ethanol in the methanol feed to the carbonylation reactor is controlled to less than or equal to 150 ppmp. In embodiments, if present, the concentration of ethanol in the methanol feed to the reactor is less than or equal to 100 ppmp, or 50 ppmp, or 25 ppmp.

Applicant has further discovered that the formation of ethyl iodide can be affected by numerous variables, including the concentration of acetaldehyde, ethyl acetate, methyl acetate, and methyl iodide in the reaction medium. Additionally, it has been found that the ethanol content in the methanol source, the hydrogen partial pressure and the hydrogen content in the carbon monoxide source affect the concentration of ethyl iodide in the reaction medium and, consequently, , the concentration of propionic acid in the final acetic acid product.

In embodiments, the concentration of ethyl iodide in the reaction medium is maintained / controlled to be less than or equal to 750 ppmp, or less than or equal to 650 ppmp, or less than or equal to 550 ppmp, or less than or equal to 450 ppmp, or less than or equal to 350 ppmp. In alternative embodiments, the concentration of ethyl iodide in the reaction medium is maintained / controlled to be greater than or equal to 1 ppmp, or 5 ppmp, or 10 ppmp, or 20 ppmp, or 25 ppmp, and less than or equal to 650 ppmp, or 550 ppmp, or 450 ppmp, or 350 ppmp.

In embodiments, the concentration of propionic acid in the acetic acid product can additionally be kept below 250 ppmp by keeping the concentration of ethyl iodide in the reaction medium less than or equal to 750 ppmp without removing propionic acid from the acetic acid product .

In embodiments, the concentration of ethyl iodide in the reaction medium and that of propionic acid in the acetic acid product may be present in a weight ratio of 3: 1 to 1: 2, or 5: 2 to 1: 2, or from 2: 1 to 1: 2. In embodiments, the concentration of acetaldehyde: ethyl iodide in the reaction medium is maintained at a weight ratio of from 2: 1 to 20: 1, or from 15: 1 to 2: 1, or from 9: 1 to 2: 1.

In embodiments, the concentration of ethyl iodide in the reaction medium can be maintained by controlling at least one of the hydrogen partial pressure, the concentration of methyl acetate, the concentration of methyl iodide and / or the concentration of acetaldehyde in the reaction medium.

A series of experiments conducted to determine the effect of acetaldehyde and other reaction conditions on the formation of ethyl iodide indicated a relationship between the concentration of acetaldehyde and the concentration of ethyl iodide in the reaction medium, as well as relationships between the concentration of the ethyl iodide reactor and the concentration of propionic acid in the final acetic acid product. In general, an ethyl iodide concentration of less than 750 ppmp and an acetaldehyde concentration of less than 1500 ppmp in the reaction medium resulted in propionic acid concentrations of less than 250 ppmp in the acetic acid product.

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Claims (11)

1. A process for producing acetic acid comprising: carbonylate at least one reagent selected from the group consisting of methanol, dimethyl ether, methyl acetate and mixtures thereof, in the presence of 0.1 to 14 wt% water, a metal catalyst, methyl iodide and salt iodide to form a reaction medium in a reactor; separating the reaction medium into a recycled liquid and a vapor product stream including acetic acid, methyl iodide, methyl acetate and water; condensing a first portion of the steam product stream to form a liquid stream; feeding a second portion of the steam product stream to a first column; feeding at least a portion of the liquid stream to the first column; Y extracting a side stream from the first column comprising an acetic acid product; wherein the liquid stream is fed to the first column above the feed of the second portion of the steam product stream and wherein the liquid stream is fed to the first column below the point where the side stream comprising the acetic acid product is drawn from the first column. 2. The process of claim 1, wherein from 1 to 50% by weight of the steam product stream is condensed to form the liquid stream, and wherein from 50 to 99% by weight of the steam stream steam product is fed to the first column. 3. The process of claim 1, wherein at least 10% by weight of the liquid stream is fed to the first column. 4. The process of claim 1, further comprising: feeding the side stream comprising the acetic acid product to a second column to obtain a purified acetic acid product. 5. The process of claim 4, wherein at least a portion of the liquid stream is introduced into the second column. The process of claim 1, wherein the reaction is performed while maintaining the reaction medium at concentrations of iodide salt from 1 to 25% by weight, methyl iodide from 1 to 25% by weight, acetate of methyl from 0.5 to 30% by weight and water from 0.1 to 14% by weight. 7. The process of claim 1, wherein the reactor further comprises a cooling unit. 8. The process of claim 1, wherein the liquid stream comprises acetic acid from 65 to 95% by weight. 9. The process of claim 1, wherein the liquid stream is enriched in acetic acid compared to the second portion of the steam product stream. 10. The process of claim 1, wherein The step of separating the reaction medium into the recycled liquid and the steam product stream is performed in an instant vaporization vessel having an upper wash section, and the process further comprises condensing a first portion of the steam product stream to form a liquid product stream; feeding a second portion of the steam product stream to a first column; extracting a side stream comprising an acetic acid product from the first column; feed the side stream to a second column; feeding at least a portion of the liquid product stream to the second column; and obtaining a purified acetic acid product from the second column. The process of claim 10, further comprising directing a bottom stream from the first column, a bottom stream from the second column, a head product stream from the second column, or a combination thereof, in the upper washing tower section in an amount sufficient to remove at least a portion of the catalyst entrained in the steam product stream.